Fluid required in treating a patient must often be stored in comparatively cool to cold temperatures with respect to the patient's body temperature. This often refrigerated storage is necessary to preserve the fluids in a state so the function and integrity of the fluid is maintained. Fluids such as blood and other bodily fluids are typically stored at hypothermic temperatures ranging from 2° to 20° Celsius. Therefore, when introducing fluids into the patient's body it is often necessary to heat the fluid to an appropriate temperature not only to prevent any rapid decrease in the patient's body temperature, but also to ensure that the fluid being introduced can function as needed. It is known that the injection of cold fluids into a patient's body can create a major source of conductive heat loss within the patient, often placing the patient at further risk by cooling, too quickly or, to a temperature where physiological damage can occur.
In heating or warming the fluid, however, care must be taken to ensure that the heating itself does not create a further complication. For instance, if blood reaches a certain temperature then hemolysis, the destruction or severe degradation, of the blood cells can occur. Likewise, if the fluid is heated too high and then introduced into the patient's body, physiological damage resulting from exposure to excessive temperatures such as burns or other such scarring can occur. Heating the fluid in bulk form usually requires the application of too intense a heat source in order to heat the entire fluid with any level of time efficiency. Likewise, heating the fluid over a prolonged period of time can lead to increased exposure of the material to the environment creating risks of contamination.
Getting the fluid into the patient requires adjustable flow so that the proper amount of fluid depending upon the need is provided to the patient. Combining the fluid delivery means with the proper and efficient heating of the fluid is crucial to the proper delivery of fluid to the patient. The prior art contains systems for warming fluids as they are infused into a patient. The manner in which the fluids are heated within these systems varies and can be accomplished via convection or conduction. An example of a system which poses clinical problems heats the fluid being delivered to the patient via exposure to a heated fluid, such as water. Such systems are usually cumbersome, require frequent cleaning, and can pollute the clinical environment through the introduction of an additional substance—the heating liquid. Such a system often places a conduit through a liquid such as water, which is then heated, and the fluid to be delivered to the patient is drawn through the conduit thereby increasing the temperature of the fluid to be delivered. Such a system can be deleterious to a sterile environment and may not be properly transported. Furthermore, these systems also have large mass, which require significant power to heat that mass yielding a significant time to achieve that temperature, or achieve a stasis when a cold mass (like a bag of chilled fluid) is introduced. An additional problem to be avoided is the danger to the patient caused by current leakage in the system circuitry and specifically the circuitry used to achieve the warming characteristics that may be in close contact to the blood being infused to the patient. Capacitive coupling, the transfer of energy from one element to another by means of mutual capacitance, could possibly cause enough current leakage to the heating system, and, potentially, to the patient and cause electric shock. It is, therefore, important to reduce the amount of capacitive coupling between the heating system and the heating exchanger, thus reducing the potential for current leakage and reducing the risk of causing electric shock to the patient, while at the same time creating efficient heating of the blood.
Moreover, during some fluid infusion procedures it is beneficial to adjust the temperature of the patient's body either warmer or cooler. As such, it is extremely beneficial to have an adjustable in-line fluid warming or cooling system so that the proper temperature can be regulated. In instances of massive or emergent fluid loss, it is often necessary to infuse (and sometimes recover and re-infuse) extremely large amounts of fluid into the patient's body. In such instances, traditional fluid heating systems often place the fluid at risk by exposure to temperatures which could damage the fluid because the fluid must be heated so rapidly. Furthermore, whereas existing patient cooling methods include practices such as externally applying cooling blankets, it will be beneficial to provide a system that more efficiently and rapidly cools a patient's core body temperature. Such problems remain largely unsolved by the art; and the need for better in-line fluid infusers is abundant.
Similarly, studies have shown that symptoms and harmful effects of certain conditions may be reduced by inducing hypothermia. For example, it has been demonstrated that circulating cooled blood before or during ischemia reduces the infarct size or slows the effects caused by infarction. Similarly, other studies show that cooling patients after suffering an acute stroke reduces metabolism and inflammation, both factors affecting ischemia induced by stroke. Thus, there also exists a need for a means to accurately cool fluid, like blood, and control flow rates of the cooled fluid.
When introducing fluid into a patient's body (e.g., the circulatory system) it is crucial that air not be introduced into the patient's body as well. Introduction of air or air bubbles into a patient's body (e.g., the circulatory system) can cause extremely deleterious effects. Air embolisms can occur if air accumulates in a patient's blood stream resulting in cardiac arrhythmias, stroke, or pulmonary infarct. Any of these potential infirmities can be life threatening and need to be minimized in situations where high volumes of fluid are being infused. It is therefore extremely important that during infusion of fluid that both the monitoring of air in the infusion system occurs to prevent introduction into the patient's body.
Devices in the prior art seeking to warm fluid for infusion into the body often suffer from very specific problems. For example, the heater system described in U.S. Pat. No. 3,590,215 issued to Anderson et al. uses regions of differing heat which the fluid encounters as it progresses through the system. Specifically, the heating element or elements described in Anderson et al. diminishes the heat in the material warming the fluid from a hottest temperature where the fluid enters the heat exchanger to a coolest temperature where the fluid exits the heat exchanger. Such a configuration not only makes it difficult to regulate the temperature of the fluid as the flow rate changes, but it also runs the risk of having to expose the fluid to temperatures above which the fluid should be exposed to, running the risk of damaging the fluid.
Likewise, the serpentine fluid flow path described in Anderson et al. creates the typical laminar type flow seen in most heat exchanger systems. For example. U.S. Pat. No. 5,245,693 to Ford et al. describes a serpentine flow pattern which is long compared to its width and wider compared to its depth. This type of flow is consistent with a non-turbulent laminar type flow path. A non-turbulent flow path requires additional heat energy to be introduced into the fluid system or longer exposure to the heating in order to increase the temperature of the fluid system uniformly to a desired temperature.
In addition to heating the fluid efficiently, a variety of clinical circumstances, including massive trauma, major surgical procedures, massive burns, and certain disease states such as pancreatitis and diabetic ketoacidosis can produce profound circulatory volume depletion, either from actual blood loss or from internal fluid imbalance. In these clinical settings, it is often necessary to infuse blood or other fluids rapidly into a patient to avert serious consequences.
Intravenous infusion rates may be defined as either routine, generally up to about 999 cubic centimeters per hour, or rapid, generally between about 999 cubic centimeters per hour and about 90,000 cubic centimeters per hour (1.5 liters per minute) or higher. Most existing infusion pumps are designed for medication delivery and are limited in their performance to the routine range of infusion rates. Such pumps are not capable of rapid intravenous infusion. Although some prior infusion systems can deliver rapid infusion, those prior rapid infusion devices are physically large, complex systems that require dedicated operation by skilled technicians. For example, U.S. Pat. No. 6,942,637 issued to Cartledge et al. describes a rapid infusion system having a differential drive that interacts with multiple motors to achieve the variable pumping rates desired. U.S. Pat. No. 6,942,637 specifically describes a differential drive that includes, among other components, multiple motors, such as a high speed motor and a stepper motor, and a combination of gears mechanically linking the multiple motors to a common drive shaft.
In other uses, a fluid pump system may be used for fluid delivery during certain surgical procedures, such as arthroscopic surgeries, to distend the area of operation. For example, saline solution is infused into the joint during an arthroscopy to expand the joint and clear the surgical field of view. However, current technologies are deficient in allowing the control of both the pressure and temperature of the fluid so as to not cause excessive cooling or warming of the area.
Accordingly, what is needed is a pump device for variably controlling fluid flow rates, fluid flow pressures, and fluid temperatures that is compact and easily operated by medical personnel in the course of their other duties. What is also needed is a low-to-high speed pump device that may heat or cool fluid efficiently and safely, that utilizes a sterile, disposable fluid containment system that can be readily attached and removed from a separate pumping mechanism.